1. Field of the Art
This invention relates to a process for producing an .alpha.-olefin polymer having high stereoregularity, excellent polymer properties and reduced odor in a high yield at a possible elevated polymerization temperature. More particularly, this invention relates to a process for polymerizing an .alpha.-olefin characterized by the use as a transition metal component of a Ziegler catalyst of a specific solid catalyst component which is obtained through a preliminary polymerization conducted under specific conditions.
2. Prior Art
It has been known in the art to polymerize an .alpha.-olefin having 3 or more carbon atoms using a catalyst component comprising a titanium compound supported on a magnesium compound. Further, it has been known that a polyolefin having some improved stereoregularity can be obtained by using the above mentioned catalyst component prepared by particular methods, and a number of inventions concerning such methods have been proposed.
In these prior art techniques, the catalyst activity is high to some extent, but the polymer properties of the polymer produced are not entirely satisfactory and improvements thereof have been desired. The polymer properties are extremely important in polymerization processes such as slurry polymerization, and gas phase polymerization. If the polymer properties are poor, polymer adhesion within the polymerization vessel or difficulty in polymer withdrawal from the polymerization vessel, etc., may be caused.
Also, the polymer concentration within a polymerization vessel is intimately related with the polymer properties and cannot be made high unless the polymer properties are good. It is very disadvantageous in industrial production when the polymer concentration cannot be made high.
Another problem involved in the prior art is an odor of polymer. The odor of polymer, the cause of which is still not well known, makes the practical use of a polymer difficult depending on the level of odor. In most cases in the practical production of a polymer the problem of polymer odor is so serious as to require some treatments and, in fact, a deodorizing treatment is usually conducted. Thus, the development of a catalyst which will provide a polymer with improved odor has been desired.
In Japanese Patent Publication No. 45,244/1982 is proposed a process wherein a preliminary polymerization is conducted in the presence of a catalyst system which consists of a solid catalyst component comprising a magnesium compound, a titanium compound and an electron donor and an organoaluminum compound. In this process about 100 moles or more of an .alpha.-olefin having 3 or more carbon atoms is preliminarily polymerized per mol of the titanium component in the solid catalyst component. For carrying out this preliminary polymerization is required an additional polymerization vessel, which means the need of an extra equipment investment in the industrial operation.
Japanese Patent Publications Nos. 11,085/64 and 32,312/72 also disclose the technique of preliminary polymerization. In these inventions, however, the amount of polymer produced in the preliminary polymerization is considerably much, which is disadvantageous in the production in an industrial scale. It is preferable in the industrial operation to reduce the amount of polymer to be produced in the preliminary polymerization. If the amount can be reduced, an extra equipment investment can be avoided.
In Japanese Patent Publication No. 151,602/82 is proposed a process wherein a preliminary polymerization is conducted such that the amount of polymer produced in the preliminary polymerization is 0.01 to 1 gram per gram of the solid catalyst component used and then the successive polymerization is conducted. However, this process appears still inadequate to improve the above mentioned properties of a polymer.